Many motor vehicle front bumper systems utilize crush cans between the bumper beam and the vehicle frame. The crush cans are engineered to deform in a predictable fashion when subjected to compressive force during a relatively high-speed frontal collision in order to absorb kinetic energy. By design, the crush cans only deform when the crash/impact is of such a severity (in terms of the level of deceleration experienced by the vehicle) that other occupant safety systems alone may not be able to adequately protect the occupants.
In a collision between a motor vehicle and a pedestrian, the force applied to the vehicle bumper is usually well below that which will result in deformation of the crush cans, so that the cans offer no protection to the pedestrian. Other features or devices may be provided to reduce the likelihood and/or severity of injury experienced by a pedestrian.
Vehicle-mounted systems have been proposed using some type of sensor (contact, radar, lidar, optical, etc.) to detect and/or predict a collision with a pedestrian. When a pedestrian collision is detected or predicted, some sort of countermeasure is activated or deployed to moderate the impact experienced by the pedestrian. Such systems require complicated sensors and electromechanical systems to function properly and reliably.